a) Field of the Invention
The present invention relates to pattern inspection for detecting any defect on patterns, specifically fine patterns formed on reticles, masks, or wafers.
In this specification, the term "design data" means both primary and secondary design data. The primary design data is data first prepared for generating a design pattern achieving a design object, and the secondary design data is data generated by editing the primary design data so as to match a specific application, such as exposure data. It is often convenient for defect inspection of real patterns to use exposure pattern data whose storage position is arranged in correspondence with the physical positions of real patterns. For example, data of the MEBES format of ETEC Corp is used. Such data is also called "design data".
b) Description of the Related Art
Patterns of semiconductor integrated circuit devices, liquid crystal display devices, plasma display devices, and other devices are becoming highly dense and integrated. As circuit patterns become complicated, the pattern data amount increases and pattern defects are likely to occur. Since pattern defects may lead to fatal troubles of circuits, pattern defect inspection is essential.
One pattern defect inspection method is to compare a plurality of same real patterns formed. For example, if a plurality of same semiconductor devices are formed on a single semiconductor wafer, there are a plurality of chips having the same pattern. Inspection through comparison between chips is called die-to-die inspection. If a plurality of reticles having the same pattern are produced, patterns of reticles are compared. This inspection is called plate-to-plate inspection.
Inspection through comparison between same patterns can be conducted at relatively high speed by using a plurality of image pick-up optical systems. However, it cannot be judged through die-to-die or plate-to-plate inspection whether a real pattern is coincident with a design pattern. For example, if some of a design pattern are not transferred to a plurality of real patterns, or if an optical system is attached with a foreign particle or the like, and this shape is transferred to a plurality of real patterns at the same position, then these defects cannot be detected and the real patterns are judged as being normal. Dies and plates are not necessary to be discriminated therebetween for the purpose of defect inspection. Therefore, both are collectively called a die hereinafter unless it is specifically used.
One method of judging whether a real pattern is coincident with a design pattern is die-to-database inspection which compares real patterns with design data. Data of such a database generally for a format suitable for the design of patterns, and so an inspection system cannot use it directly. For example, design data for an exposure pattern is made generally more sophisticated and at a higher resolution than design data for other application uses. A plurality of dots on an exposure pattern may be combined to produce one dot for comparison with another pattern. Sometimes the design data can be used for comparison with real patterns only after some proper data processing such as reduction/magnification, rotation, and inversion is executed.
It is therefore necessary to convert the format of design data into a format suitable for die-to-database inspection. All design data of a pattern to be inspected have been conventionally converted at one time collectively to form an inspection database, both in the case of the primary design data and of the secondary design data, such as exposure design data.
Design data is generally formed to have the same size as a real pattern. Reticles are formed at various magnification factors of, for example, 1, 2, 2.5, 4, 5, and 10. A single reticle may sometimes have areas of different magnification factors. Therefore, at each manufacture process, a reticle having a suitable pattern magnification factor has been selected and inspection data matching the pattern magnification factor has been generated.
It takes a very long time to convert design data into inspection data. If design data is missed during the conversion process, the whole conversion process must start again from the beginning. As the integration degree of a pattern rises and the pattern data amount increases, the data conversion time becomes very long. Since an immense amount of design data is processed, it becomes necessary to use a computing system of a large capacity, such as computers and memories. If all the design data and converted inspection data cannot be loaded in a storage unit, it becomes necessary to generate divided portions of inspection data and to perform inspection a plurality of times.